import sequtils,algorithm,strutils,intsets,tables
template times*(n:int,body) = (for _ in 0..<n: body)

proc getchar_unlocked():char {. importc:"getchar_unlocked",header: "<stdio.h>" .}
proc scan(): int =
  while true:
    let k = getchar_unlocked()
    if k < '0': break
    result = 10 * result + k.ord - '0'.ord


let n = scan()
let m = scan()
let k = scan()
# a -> c -> b
var P = newSeqWith(n+1,newTable[int,seq[int]]())
m.times:
  let a = scan()
  let b = scan()
  let c = scan()
  if c notin P[a]: P[a][c] = @[]
  if c notin P[b]: P[b][c] = @[]
  P[a][c] &= b
  P[b][c] &= a
let C = newSeqWith(k,scan())
var nows = initIntSet()
for a in 1..n:
  if C[0] notin P[a] : continue
  for b in P[a][C[0]]:
    nows.incl b
for i in 1..<k:
  var nexts = initIntSet()
  for a in nows:
    if C[i] notin P[a] : continue
    for b in P[a][C[i]]:
      nexts.incl b
  nows = nexts
echo nows.card
echo toSeq(nows.items).sorted(cmp).mapIt($it).join(" ")